Introduction

R Markdown Preamble

This is an R Markdown document. Markdown is a simple formatting syntax for authoring HTML, PDF, and MS Word documents. For more details on using R Markdown see http://rmarkdown.rstudio.com.

See also the R Markdown Cookbook)

When you click the Knit button a document will be generated that includes both content as well as the output of any embedded R code chunks within the document. You can embed an R code chunk like this:

Sample Inbuilt Data Set

summary(cars)
##      speed           dist       
##  Min.   : 4.0   Min.   :  2.00  
##  1st Qu.:12.0   1st Qu.: 26.00  
##  Median :15.0   Median : 36.00  
##  Mean   :15.4   Mean   : 42.98  
##  3rd Qu.:19.0   3rd Qu.: 56.00  
##  Max.   :25.0   Max.   :120.00

Including Plots - Example

Embed Plot

You can also embed plots, for example:

Note that the echo = FALSE parameter was added to the code chunk to prevent printing of the R code that generated the plot.

Another Plot

Let’s create another Test plot

plot(cars,  col = "red", xlab = "Speed (mph)", ylab = "Distance (miles)" )

A summary of the data frame is given below

pacman::p_load(knitr)
kable(summary(cars))
speed dist
Min. : 4.0 Min. : 2.00
1st Qu.:12.0 1st Qu.: 26.00
Median :15.0 Median : 36.00
Mean :15.4 Mean : 42.98
3rd Qu.:19.0 3rd Qu.: 56.00
Max. :25.0 Max. :120.00

Start of My SHC 798 R-code

R basics

  1. Why install Rtools?

  2. R Shiny Gallery: There’s Shiny for R and Shiny for Python

R Operations 1

What can be done?

# R as a calculator
sqrt(12)
## [1] 3.464102
x <- 3
y <- x^2
x+y
## [1] 12
# Creating Vectors
v1 <- c(1,5, 80)
v1
## [1]  1  5 80
v2 <- 2:11
v2
##  [1]  2  3  4  5  6  7  8  9 10 11
a <- c(1,6,10,22,7,13)
mean(a)
## [1] 9.833333
# Incomplete Statement
3*(4 +
     +2)
## [1] 18
#Assignments and Function Calls
t.a <- 3*(4+2)
t.b <- t.a + 2.5
mn <- mean(c(t.a,t.b))
mn
## [1] 19.25

R Help

Resources

  1. Very useful and helpful R Q&A Website

  2. Paradis 2005 - R for Beginners [Textbook]

  3. R Reference Card [in the notes, 6 pages - Material from R for Beginners]

  4. Base R Cheat Sheet [in the notes, 2 pages]

  5. Venables et al 2017 - An introduction to R [Textbook]

  6. R for Data Science, r4ds or the r4ds-2e

  7. W3Schools R Certification

Snippet from Resource 4
Snippet from Resource 4

R Operations 2

Importing Data sets

# Import Data: Website
url <- "https://stat.ethz.ch/Teaching/Datasets/WBL/sport.dat"
d.sport <- read.table(url, header = TRUE)
head(d.sport)
##            weit kugel hoch  disc stab speer punkte
## OBRIEN     7.57 15.66  207 48.78  500 66.90   8824
## BUSEMANN   8.07 13.60  204 45.04  480 66.86   8706
## DVORAK     7.60 15.82  198 46.28  470 70.16   8664
## FRITZ      7.77 15.31  204 49.84  510 65.70   8644
## HAMALAINEN 7.48 16.32  198 49.62  500 57.66   8613
## NOOL       7.88 14.01  201 42.98  540 65.48   8543
# Setting the Working Directory
# Use:
getwd() #Prints the current working directory
## [1] "D:/2025 MEng Transportation/SHC 798 R-Proj"
# setwd("D:/2025 MEng Transportation/SHC 798 R-Proj") ~ Sets the working directory
# Alternatively, use “Session” → “Set Working Directory” → “Choose Directory…”
# Import Data: Files
  # - Different ways depending on the format (csv, txt, xlsx, etc.) 
  # - Alternative: use the “Import Dataset” tool in RStudio (upper-right panel)
# Save data or write data to a file
  # - Text files
  # - Excel files: use CSV

R Objects & Indexing

# R Objects: Data frames (Most essential)
str(d.sport)
## 'data.frame':    15 obs. of  7 variables:
##  $ weit  : num  7.57 8.07 7.6 7.77 7.48 7.88 7.64 7.61 7.27 7.49 ...
##  $ kugel : num  15.7 13.6 15.8 15.3 16.3 ...
##  $ hoch  : int  207 204 198 204 198 201 195 213 207 204 ...
##  $ disc  : num  48.8 45 46.3 49.8 49.6 ...
##  $ stab  : int  500 480 470 510 500 540 540 520 470 470 ...
##  $ speer : num  66.9 66.9 70.2 65.7 57.7 ...
##  $ punkte: int  8824 8706 8664 8644 8613 8543 8422 8318 8307 8300 ...
# R Objects: Vectors
  # (e.g., a column from the data set d.sport)
kugel <- d.sport$kugel
str(kugel)
##  num [1:15] 15.7 13.6 15.8 15.3 16.3 ...
participant <- rownames(d.sport)
str(participant)
##  chr [1:15] "OBRIEN" "BUSEMANN" "DVORAK" "FRITZ" "HAMALAINEN" "NOOL" ...
# Select elements
participant[4]
## [1] "FRITZ"
d.sport[c(3,6,4), c(1:3,7)]
##        weit kugel hoch punkte
## DVORAK 7.60 15.82  198   8664
## NOOL   7.88 14.01  201   8543
## FRITZ  7.77 15.31  204   8644
d.sport["FRITZ", ]
##       weit kugel hoch  disc stab speer punkte
## FRITZ 7.77 15.31  204 49.84  510  65.7   8644
# Accessing Parts of an Object
# To access only part of an object, use []
  # For vectors: myvector[x]
  # For two-dimensional objects, e.g. data frames or matrices: mydata.frame[x,y]
d.sport[ , ]
##            weit kugel hoch  disc stab speer punkte
## OBRIEN     7.57 15.66  207 48.78  500 66.90   8824
## BUSEMANN   8.07 13.60  204 45.04  480 66.86   8706
## DVORAK     7.60 15.82  198 46.28  470 70.16   8664
## FRITZ      7.77 15.31  204 49.84  510 65.70   8644
## HAMALAINEN 7.48 16.32  198 49.62  500 57.66   8613
## NOOL       7.88 14.01  201 42.98  540 65.48   8543
## ZMELIK     7.64 13.53  195 43.44  540 67.20   8422
## GANIYEV    7.61 14.71  213 44.86  520 53.70   8318
## PENALVER   7.27 16.91  207 48.92  470 57.08   8307
## HUFFINS    7.49 15.57  204 48.72  470 60.62   8300
## PLAZIAT    7.82 14.85  204 45.34  490 52.18   8282
## MAGNUSSON  7.28 15.52  195 43.78  480 61.10   8274
## SMITH      7.47 16.97  195 49.54  500 64.34   8271
## MUELLER    7.25 14.69  195 45.90  510 66.10   8253
## CHMARA     7.75 14.51  210 42.60  490 54.84   8249
c(1,3,7)
## [1] 1 3 7
1:10
##  [1]  1  2  3  4  5  6  7  8  9 10
d.sport[1:10, ]
##            weit kugel hoch  disc stab speer punkte
## OBRIEN     7.57 15.66  207 48.78  500 66.90   8824
## BUSEMANN   8.07 13.60  204 45.04  480 66.86   8706
## DVORAK     7.60 15.82  198 46.28  470 70.16   8664
## FRITZ      7.77 15.31  204 49.84  510 65.70   8644
## HAMALAINEN 7.48 16.32  198 49.62  500 57.66   8613
## NOOL       7.88 14.01  201 42.98  540 65.48   8543
## ZMELIK     7.64 13.53  195 43.44  540 67.20   8422
## GANIYEV    7.61 14.71  213 44.86  520 53.70   8318
## PENALVER   7.27 16.91  207 48.92  470 57.08   8307
## HUFFINS    7.49 15.57  204 48.72  470 60.62   8300
d.sport[-c(1, 3,7), ] #negative indices are excluded
##            weit kugel hoch  disc stab speer punkte
## BUSEMANN   8.07 13.60  204 45.04  480 66.86   8706
## FRITZ      7.77 15.31  204 49.84  510 65.70   8644
## HAMALAINEN 7.48 16.32  198 49.62  500 57.66   8613
## NOOL       7.88 14.01  201 42.98  540 65.48   8543
## GANIYEV    7.61 14.71  213 44.86  520 53.70   8318
## PENALVER   7.27 16.91  207 48.92  470 57.08   8307
## HUFFINS    7.49 15.57  204 48.72  470 60.62   8300
## PLAZIAT    7.82 14.85  204 45.34  490 52.18   8282
## MAGNUSSON  7.28 15.52  195 43.78  480 61.10   8274
## SMITH      7.47 16.97  195 49.54  500 64.34   8271
## MUELLER    7.25 14.69  195 45.90  510 66.10   8253
## CHMARA     7.75 14.51  210 42.60  490 54.84   8249
d.sport[ , 2:3]
##            kugel hoch
## OBRIEN     15.66  207
## BUSEMANN   13.60  204
## DVORAK     15.82  198
## FRITZ      15.31  204
## HAMALAINEN 16.32  198
## NOOL       14.01  201
## ZMELIK     13.53  195
## GANIYEV    14.71  213
## PENALVER   16.91  207
## HUFFINS    15.57  204
## PLAZIAT    14.85  204
## MAGNUSSON  15.52  195
## SMITH      16.97  195
## MUELLER    14.69  195
## CHMARA     14.51  210
d.sport[c(1,3,6), 2:3]
##        kugel hoch
## OBRIEN 15.66  207
## DVORAK 15.82  198
## NOOL   14.01  201
# Function Calls
mean(kugel)
## [1] 15.19867
quantile(kugel)
##    0%   25%   50%   75%  100% 
## 13.53 14.60 15.31 15.74 16.97
quantile(kugel,probs = c(.75, 0.9))
##    75%    90% 
## 15.740 16.674
# Functions consist of mandatory and optional arguments:
  # mean(x, trim = 0, na.rm = FALSE, …)
  # x: mandatory argument
  # trim: optional argument, default is 0
  # na.rm: optional argument, default is FALSE

# The arguments of a function have a defined order and each argument has its own unique name
mean(x = kugel, na.rm = TRUE)
## [1] 15.19867
mean(x = kugel, ,TRUE)
## [1] 15.19867
# Useful Functions
nrow(d.sport)
## [1] 15
ncol(d.sport)
## [1] 7
dim(d.sport)
## [1] 15  7
summary(d.sport)
##       weit           kugel            hoch            disc            stab    
##  Min.   :7.250   Min.   :13.53   Min.   :195.0   Min.   :42.60   Min.   :470  
##  1st Qu.:7.475   1st Qu.:14.60   1st Qu.:196.5   1st Qu.:44.32   1st Qu.:480  
##  Median :7.600   Median :15.31   Median :204.0   Median :45.90   Median :500  
##  Mean   :7.597   Mean   :15.20   Mean   :202.0   Mean   :46.38   Mean   :498  
##  3rd Qu.:7.760   3rd Qu.:15.74   3rd Qu.:205.5   3rd Qu.:48.85   3rd Qu.:510  
##  Max.   :8.070   Max.   :16.97   Max.   :213.0   Max.   :49.84   Max.   :540  
##      speer           punkte    
##  Min.   :52.18   Min.   :8249  
##  1st Qu.:57.37   1st Qu.:8278  
##  Median :64.34   Median :8318  
##  Mean   :61.99   Mean   :8445  
##  3rd Qu.:66.48   3rd Qu.:8628  
##  Max.   :70.16   Max.   :8824
# apply(d.sport)
head(d.sport)
##            weit kugel hoch  disc stab speer punkte
## OBRIEN     7.57 15.66  207 48.78  500 66.90   8824
## BUSEMANN   8.07 13.60  204 45.04  480 66.86   8706
## DVORAK     7.60 15.82  198 46.28  470 70.16   8664
## FRITZ      7.77 15.31  204 49.84  510 65.70   8644
## HAMALAINEN 7.48 16.32  198 49.62  500 57.66   8613
## NOOL       7.88 14.01  201 42.98  540 65.48   8543
tail(d.sport)
##           weit kugel hoch  disc stab speer punkte
## HUFFINS   7.49 15.57  204 48.72  470 60.62   8300
## PLAZIAT   7.82 14.85  204 45.34  490 52.18   8282
## MAGNUSSON 7.28 15.52  195 43.78  480 61.10   8274
## SMITH     7.47 16.97  195 49.54  500 64.34   8271
## MUELLER   7.25 14.69  195 45.90  510 66.10   8253
## CHMARA    7.75 14.51  210 42.60  490 54.84   8249

R Packages

#install.packages("MASS")
#require(MASS) # for every R Session
#library(MASS) # or use this

Online resources: University of Pretoria | SHC 798 | Introduction to R 36

o List of all packages: http://cran.r-project.org/web/packages/

o By topic: http://cran.r-project.org/web/views/

o Ask Google / ChatGPT / GroK

Missing Values

d.sport.NA <- d.sport
d.sport.NA[2, "kugel"] <- NA 
d.sport.NA[3, "hoch"] <- -999
# missing values are coded as NA (not available) and are treated in a special way, e.g. is.na():
is.na(d.sport.NA) #one logical value per element
##             weit kugel  hoch  disc  stab speer punkte
## OBRIEN     FALSE FALSE FALSE FALSE FALSE FALSE  FALSE
## BUSEMANN   FALSE  TRUE FALSE FALSE FALSE FALSE  FALSE
## DVORAK     FALSE FALSE FALSE FALSE FALSE FALSE  FALSE
## FRITZ      FALSE FALSE FALSE FALSE FALSE FALSE  FALSE
## HAMALAINEN FALSE FALSE FALSE FALSE FALSE FALSE  FALSE
## NOOL       FALSE FALSE FALSE FALSE FALSE FALSE  FALSE
## ZMELIK     FALSE FALSE FALSE FALSE FALSE FALSE  FALSE
## GANIYEV    FALSE FALSE FALSE FALSE FALSE FALSE  FALSE
## PENALVER   FALSE FALSE FALSE FALSE FALSE FALSE  FALSE
## HUFFINS    FALSE FALSE FALSE FALSE FALSE FALSE  FALSE
## PLAZIAT    FALSE FALSE FALSE FALSE FALSE FALSE  FALSE
## MAGNUSSON  FALSE FALSE FALSE FALSE FALSE FALSE  FALSE
## SMITH      FALSE FALSE FALSE FALSE FALSE FALSE  FALSE
## MUELLER    FALSE FALSE FALSE FALSE FALSE FALSE  FALSE
## CHMARA     FALSE FALSE FALSE FALSE FALSE FALSE  FALSE
sum(is.na(d.sport.NA)) # adds up the TRUE elements
## [1] 1
which(is.na(d.sport.NA), arr.ind = TRUE) # where are the NA's
##          row col
## BUSEMANN   2   2
# Specify missing values after reading in the data:
d.sport.NA[d.sport.NA == -999] <- NA

# Many functions have an argument to handle missing values, e.g. na.rm, na.omit:
sum(d.sport.NA$kugel)
## [1] NA
sum(d.sport.NA$kugel, na.rm = TRUE)
## [1] 214.38
na.omit(d.sport.NA)
##            weit kugel hoch  disc stab speer punkte
## OBRIEN     7.57 15.66  207 48.78  500 66.90   8824
## FRITZ      7.77 15.31  204 49.84  510 65.70   8644
## HAMALAINEN 7.48 16.32  198 49.62  500 57.66   8613
## NOOL       7.88 14.01  201 42.98  540 65.48   8543
## ZMELIK     7.64 13.53  195 43.44  540 67.20   8422
## GANIYEV    7.61 14.71  213 44.86  520 53.70   8318
## PENALVER   7.27 16.91  207 48.92  470 57.08   8307
## HUFFINS    7.49 15.57  204 48.72  470 60.62   8300
## PLAZIAT    7.82 14.85  204 45.34  490 52.18   8282
## MAGNUSSON  7.28 15.52  195 43.78  480 61.10   8274
## SMITH      7.47 16.97  195 49.54  500 64.34   8271
## MUELLER    7.25 14.69  195 45.90  510 66.10   8253
## CHMARA     7.75 14.51  210 42.60  490 54.84   8249

Basic Graphics

# The Plot Function: only 1 mandatory argument i.e., x. The 2nd most important one is y. 
  # many optional arguments [col,pch,main,cex, ...]
  # use function par (?par) to set or query graphical parameters

data(iris)
iris
##     Sepal.Length Sepal.Width Petal.Length Petal.Width    Species
## 1            5.1         3.5          1.4         0.2     setosa
## 2            4.9         3.0          1.4         0.2     setosa
## 3            4.7         3.2          1.3         0.2     setosa
## 4            4.6         3.1          1.5         0.2     setosa
## 5            5.0         3.6          1.4         0.2     setosa
## 6            5.4         3.9          1.7         0.4     setosa
## 7            4.6         3.4          1.4         0.3     setosa
## 8            5.0         3.4          1.5         0.2     setosa
## 9            4.4         2.9          1.4         0.2     setosa
## 10           4.9         3.1          1.5         0.1     setosa
## 11           5.4         3.7          1.5         0.2     setosa
## 12           4.8         3.4          1.6         0.2     setosa
## 13           4.8         3.0          1.4         0.1     setosa
## 14           4.3         3.0          1.1         0.1     setosa
## 15           5.8         4.0          1.2         0.2     setosa
## 16           5.7         4.4          1.5         0.4     setosa
## 17           5.4         3.9          1.3         0.4     setosa
## 18           5.1         3.5          1.4         0.3     setosa
## 19           5.7         3.8          1.7         0.3     setosa
## 20           5.1         3.8          1.5         0.3     setosa
## 21           5.4         3.4          1.7         0.2     setosa
## 22           5.1         3.7          1.5         0.4     setosa
## 23           4.6         3.6          1.0         0.2     setosa
## 24           5.1         3.3          1.7         0.5     setosa
## 25           4.8         3.4          1.9         0.2     setosa
## 26           5.0         3.0          1.6         0.2     setosa
## 27           5.0         3.4          1.6         0.4     setosa
## 28           5.2         3.5          1.5         0.2     setosa
## 29           5.2         3.4          1.4         0.2     setosa
## 30           4.7         3.2          1.6         0.2     setosa
## 31           4.8         3.1          1.6         0.2     setosa
## 32           5.4         3.4          1.5         0.4     setosa
## 33           5.2         4.1          1.5         0.1     setosa
## 34           5.5         4.2          1.4         0.2     setosa
## 35           4.9         3.1          1.5         0.2     setosa
## 36           5.0         3.2          1.2         0.2     setosa
## 37           5.5         3.5          1.3         0.2     setosa
## 38           4.9         3.6          1.4         0.1     setosa
## 39           4.4         3.0          1.3         0.2     setosa
## 40           5.1         3.4          1.5         0.2     setosa
## 41           5.0         3.5          1.3         0.3     setosa
## 42           4.5         2.3          1.3         0.3     setosa
## 43           4.4         3.2          1.3         0.2     setosa
## 44           5.0         3.5          1.6         0.6     setosa
## 45           5.1         3.8          1.9         0.4     setosa
## 46           4.8         3.0          1.4         0.3     setosa
## 47           5.1         3.8          1.6         0.2     setosa
## 48           4.6         3.2          1.4         0.2     setosa
## 49           5.3         3.7          1.5         0.2     setosa
## 50           5.0         3.3          1.4         0.2     setosa
## 51           7.0         3.2          4.7         1.4 versicolor
## 52           6.4         3.2          4.5         1.5 versicolor
## 53           6.9         3.1          4.9         1.5 versicolor
## 54           5.5         2.3          4.0         1.3 versicolor
## 55           6.5         2.8          4.6         1.5 versicolor
## 56           5.7         2.8          4.5         1.3 versicolor
## 57           6.3         3.3          4.7         1.6 versicolor
## 58           4.9         2.4          3.3         1.0 versicolor
## 59           6.6         2.9          4.6         1.3 versicolor
## 60           5.2         2.7          3.9         1.4 versicolor
## 61           5.0         2.0          3.5         1.0 versicolor
## 62           5.9         3.0          4.2         1.5 versicolor
## 63           6.0         2.2          4.0         1.0 versicolor
## 64           6.1         2.9          4.7         1.4 versicolor
## 65           5.6         2.9          3.6         1.3 versicolor
## 66           6.7         3.1          4.4         1.4 versicolor
## 67           5.6         3.0          4.5         1.5 versicolor
## 68           5.8         2.7          4.1         1.0 versicolor
## 69           6.2         2.2          4.5         1.5 versicolor
## 70           5.6         2.5          3.9         1.1 versicolor
## 71           5.9         3.2          4.8         1.8 versicolor
## 72           6.1         2.8          4.0         1.3 versicolor
## 73           6.3         2.5          4.9         1.5 versicolor
## 74           6.1         2.8          4.7         1.2 versicolor
## 75           6.4         2.9          4.3         1.3 versicolor
## 76           6.6         3.0          4.4         1.4 versicolor
## 77           6.8         2.8          4.8         1.4 versicolor
## 78           6.7         3.0          5.0         1.7 versicolor
## 79           6.0         2.9          4.5         1.5 versicolor
## 80           5.7         2.6          3.5         1.0 versicolor
## 81           5.5         2.4          3.8         1.1 versicolor
## 82           5.5         2.4          3.7         1.0 versicolor
## 83           5.8         2.7          3.9         1.2 versicolor
## 84           6.0         2.7          5.1         1.6 versicolor
## 85           5.4         3.0          4.5         1.5 versicolor
## 86           6.0         3.4          4.5         1.6 versicolor
## 87           6.7         3.1          4.7         1.5 versicolor
## 88           6.3         2.3          4.4         1.3 versicolor
## 89           5.6         3.0          4.1         1.3 versicolor
## 90           5.5         2.5          4.0         1.3 versicolor
## 91           5.5         2.6          4.4         1.2 versicolor
## 92           6.1         3.0          4.6         1.4 versicolor
## 93           5.8         2.6          4.0         1.2 versicolor
## 94           5.0         2.3          3.3         1.0 versicolor
## 95           5.6         2.7          4.2         1.3 versicolor
## 96           5.7         3.0          4.2         1.2 versicolor
## 97           5.7         2.9          4.2         1.3 versicolor
## 98           6.2         2.9          4.3         1.3 versicolor
## 99           5.1         2.5          3.0         1.1 versicolor
## 100          5.7         2.8          4.1         1.3 versicolor
## 101          6.3         3.3          6.0         2.5  virginica
## 102          5.8         2.7          5.1         1.9  virginica
## 103          7.1         3.0          5.9         2.1  virginica
## 104          6.3         2.9          5.6         1.8  virginica
## 105          6.5         3.0          5.8         2.2  virginica
## 106          7.6         3.0          6.6         2.1  virginica
## 107          4.9         2.5          4.5         1.7  virginica
## 108          7.3         2.9          6.3         1.8  virginica
## 109          6.7         2.5          5.8         1.8  virginica
## 110          7.2         3.6          6.1         2.5  virginica
## 111          6.5         3.2          5.1         2.0  virginica
## 112          6.4         2.7          5.3         1.9  virginica
## 113          6.8         3.0          5.5         2.1  virginica
## 114          5.7         2.5          5.0         2.0  virginica
## 115          5.8         2.8          5.1         2.4  virginica
## 116          6.4         3.2          5.3         2.3  virginica
## 117          6.5         3.0          5.5         1.8  virginica
## 118          7.7         3.8          6.7         2.2  virginica
## 119          7.7         2.6          6.9         2.3  virginica
## 120          6.0         2.2          5.0         1.5  virginica
## 121          6.9         3.2          5.7         2.3  virginica
## 122          5.6         2.8          4.9         2.0  virginica
## 123          7.7         2.8          6.7         2.0  virginica
## 124          6.3         2.7          4.9         1.8  virginica
## 125          6.7         3.3          5.7         2.1  virginica
## 126          7.2         3.2          6.0         1.8  virginica
## 127          6.2         2.8          4.8         1.8  virginica
## 128          6.1         3.0          4.9         1.8  virginica
## 129          6.4         2.8          5.6         2.1  virginica
## 130          7.2         3.0          5.8         1.6  virginica
## 131          7.4         2.8          6.1         1.9  virginica
## 132          7.9         3.8          6.4         2.0  virginica
## 133          6.4         2.8          5.6         2.2  virginica
## 134          6.3         2.8          5.1         1.5  virginica
## 135          6.1         2.6          5.6         1.4  virginica
## 136          7.7         3.0          6.1         2.3  virginica
## 137          6.3         3.4          5.6         2.4  virginica
## 138          6.4         3.1          5.5         1.8  virginica
## 139          6.0         3.0          4.8         1.8  virginica
## 140          6.9         3.1          5.4         2.1  virginica
## 141          6.7         3.1          5.6         2.4  virginica
## 142          6.9         3.1          5.1         2.3  virginica
## 143          5.8         2.7          5.1         1.9  virginica
## 144          6.8         3.2          5.9         2.3  virginica
## 145          6.7         3.3          5.7         2.5  virginica
## 146          6.7         3.0          5.2         2.3  virginica
## 147          6.3         2.5          5.0         1.9  virginica
## 148          6.5         3.0          5.2         2.0  virginica
## 149          6.2         3.4          5.4         2.3  virginica
## 150          5.9         3.0          5.1         1.8  virginica
str(iris)
## 'data.frame':    150 obs. of  5 variables:
##  $ Sepal.Length: num  5.1 4.9 4.7 4.6 5 5.4 4.6 5 4.4 4.9 ...
##  $ Sepal.Width : num  3.5 3 3.2 3.1 3.6 3.9 3.4 3.4 2.9 3.1 ...
##  $ Petal.Length: num  1.4 1.4 1.3 1.5 1.4 1.7 1.4 1.5 1.4 1.5 ...
##  $ Petal.Width : num  0.2 0.2 0.2 0.2 0.2 0.4 0.3 0.2 0.2 0.1 ...
##  $ Species     : Factor w/ 3 levels "setosa","versicolor",..: 1 1 1 1 1 1 1 1 1 1 ...
# A factor represents categorical values with different "levels"
# High-level plotting function: opens a plot
plot(x = iris$Sepal.Width, y =iris$Sepal.Length, col = iris[ , "Species"], pch = 19)

#Low-level plotting functions: add to an existing plot
legend("topright", legend = levels(iris[ , "Species"]), pch = 19, col = 1:3) # adds legend

# In an Rmd file such as this one, you need to call both the plot() & legend() functions at the same time. Or they should be in the same line of code

pairs(iris[ , -5], col = iris[ , 5])

Arguments of plot

Plot Arguments
Plot Arguments

Three categories of R graphics functions:

• High-level plotting functions such as plot() to generate a new graphics display.

• Low-level plotting functions such as legend() to add further graphical elements to an existing plot.

• Interactive functions such as identify() to amend or collect information interactively from a plot.

Low-level plotting functions

Low-level plotting functions
Low-level plotting functions

Useful plot functions

  • plot, pairs, interaction.plot
  • boxplot, hist
  • plot3d

Graphical Output

pdf(file = "iris_plot.pdf") # open the graphics device
plot(Sepal.Length ~ Sepal.Width, data = iris)
# add anything else you want in your plots
dev.off() #close the graphic device
## png 
##   2

Several plots in one graphical window: splits the graphical window into 3 rows and 2 columns.

par(mfrow=c(3,2))

Other Graphics: in lattice

The lattice package functions: good for repeating graphs for various groups. See the Lattice Graphs in R (at http://www.statmethods.net/advgraphs/trellis.html) for more information.

pacman::p_load(lattice)
xyplot(Sepal.Width ~ Sepal.Length | Species, data = iris)

Other Graphics: in ggplot2

ggplot2 package: very flexible, based on grammar of graphics.

pacman::p_load(ggplot2)
ggplot(data = iris, aes(x = Sepal.Length, y = Sepal.Width)) + facet_grid(rows = ~ Species) + geom_point()

Hypothesis Testing

Approach: Hypothesis testing in 6 steps:

  1. Declare model by which data were generated (e.g. population is normally distributed, large sample size and σ not known).
  2. Define null hypothesis, H0 and alternative hypothesis, HA ; where H0 is the statement being tested in a test of (statistical) significance and HA is the statement that is hoped or expected to be true instead of the null hypothesis
  3. Choose the level of significance, α.
  4. Determine critical values for the *level of significance α and degrees of freedom, df = (n-1)
  5. Define and calculate test statistic, e.g. one-sample test:
  6. Compare the test statistic to the critical values and make decision to reject or fail to reject H0 .

Hypothesis Tests – An Example

# Is the sepal length of versicolor different to that of virginica?
#Let’s use a *t-Test and a *Wilcoxon rank-sum test.
testdata <- iris[iris$Species != "setosa", c("Sepal.Length", "Species")]
testdata$Species <- droplevels(testdata$Species)
str(testdata) # prepare and check the data
## 'data.frame':    100 obs. of  2 variables:
##  $ Sepal.Length: num  7 6.4 6.9 5.5 6.5 5.7 6.3 4.9 6.6 5.2 ...
##  $ Species     : Factor w/ 2 levels "versicolor","virginica": 1 1 1 1 1 1 1 1 1 1 ...
# Check normality assumption of t-Test using QQ-Plot:
versi.id <- testdata$Species == "versicolor"
par(mfrow=c(1,2))
qqnorm(testdata$Sepal.Length[versi.id]); qqline(testdata$Sepal.Length[versi.id])
qqnorm(testdata$Sepal.Length[!versi.id]); qqline(testdata$Sepal.Length[versi.id])

# Two-sample t-test:
versi.id <- testdata$Species == "versicolor"
t.test(x =testdata$Sepal.Length[versi.id], y = testdata$Sepal.Length[!versi.id], var.equal = TRUE)
## 
##  Two Sample t-test
## 
## data:  testdata$Sepal.Length[versi.id] and testdata$Sepal.Length[!versi.id]
## t = -5.6292, df = 98, p-value = 1.725e-07
## alternative hypothesis: true difference in means is not equal to 0
## 95 percent confidence interval:
##  -0.8818516 -0.4221484
## sample estimates:
## mean of x mean of y 
##     5.936     6.588
# T-test rejects the null hypothesis at 5% significance level.
# Do not forget to visually check the normality assumptions (QQ-plot)
# Check assumption of \*Wilcoxon Rank Test: same distribution, just a location shift.
boxplot(testdata$Sepal.Length ~ testdata$Species)

# Now, perform the test:
versi.id <- testdata$Species == "versicolor"
wilcox.test(x =testdata$Sepal.Length[versi.id], y = testdata$Sepal.Length[!versi.id], var.equal = TRUE)
## 
##  Wilcoxon rank sum test with continuity correction
## 
## data:  testdata$Sepal.Length[versi.id] and testdata$Sepal.Length[!versi.id]
## W = 526, p-value = 5.869e-07
## alternative hypothesis: true location shift is not equal to 0
# Wilcoxon Rank Test also rejects the null hypothesis at 5% significance level.

The Wilcoxon Rank Test is the preferred test for a two-sample statistical test.

Hypothesis Tests - Summary

How to proceed:

  • Formulate the null & alternative hypotheses
  • Choose the appropriate test
  • Collate data, i.e., do an experiment
  • Look at data: plot(), pairs(), hist(), boxplot()
  • Validate assumptions of test (e.g., T-test, Wilcoxon test)
  • Carry out the test and interpret result
Hypothesis Tests
Hypothesis Tests

Hypothesis Tests – Chi-squared test of independence

  • Hypothesis: H0: Independence of education and marriage status
  • HA: Dependence of education and marriage status
url <- "https://stat.ethz.ch/Teaching/Datasets/edu.txt"
d.edu <- read.table(url, header = TRUE)

# Cross-tables in R
# Count number of cases with same value:
table(d.edu[, "Married"])
## 
## Married more Married once 
##          205         1231
# Cross-table
table(d.edu[, "Education"], d.edu[, "Married"])
##             
##              Married more Married once
##   College              61          550
##   No College          144          681
# Now we perform a Chi-squared test
chisq.test(d.edu[, "Education"], d.edu[, "Married"])
## 
##  Pearson's Chi-squared test with Yates' continuity correction
## 
## data:  d.edu[, "Education"] and d.edu[, "Married"]
## X-squared = 15.405, df = 1, p-value = 8.675e-05
# Result: Reject H0, i.e. education and marriage are dependent.

Correlation

# Correlation
url1 <- "https://stat.ethz.ch/Teaching/Datasets/basischOhneNA.dat"
d.basisch <- read.table(url1, header = TRUE)
str(d.basisch)
## 'data.frame':    123 obs. of  4 variables:
##  $ ph    : num  7.33 7.69 7.9 8.14 7.62 ...
##  $ l.sar : num  0.0969 0.4393 1 1.316 0.0607 ...
##  $ height: num  5.91 5.2 4.4 4.5 6.05 6 5.35 5.55 4.95 5.2 ...
##  $ h.quad: num  34.9 27 19.4 20.2 36.6 ...
# Calculate the (Pearson) correlation of ph and height:
cor(d.basisch$ph, d.basisch$height)
## [1] -0.6925717
# Corresponding plot:
plot(d.basisch$ph, d.basisch$height)

All plots show 2 variables with a correlation of 0.7

  • one looks good
  • another does not
  • outlier(s) influence the result
  • ALWAYS FIRST LOOK AT PLOTS

Regression

Simple Linear Regression (SLR)

From the d.basisch() data,

  1. Response variable: height or h.quad: Height of trees or squared height, respectively.
  2. Possible explanatory variables: ph: pH-values of soil and l.sar: log(sodium absorption ratio)
The Simple Linear Regression Model
The Simple Linear Regression Model

Let us pick the variable ph as the explanatory variable.

# Fit to data using lm:
fit <- lm(formula = height ~ ph, data = d.basisch)
summary(fit)
## 
## Call:
## lm(formula = height ~ ph, data = d.basisch)
## 
## Residuals:
##     Min      1Q  Median      3Q     Max 
## -3.7020 -0.5471  0.0874  0.6663  2.0033 
## 
## Coefficients:
##             Estimate Std. Error t value Pr(>|t|)    
## (Intercept)  28.7227     2.2395   12.82   <2e-16 ***
## ph           -3.0034     0.2844  -10.56   <2e-16 ***
## ---
## Signif. codes:  0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1
## 
## Residual standard error: 1.008 on 121 degrees of freedom
## Multiple R-squared:  0.4797, Adjusted R-squared:  0.4754 
## F-statistic: 111.5 on 1 and 121 DF,  p-value: < 2.2e-16
# Estimated equation: height = 28.7 – 3.0pH

# Drawing line into scatterplot:
plot(d.basisch$ph, d.basisch$height) + abline(fit)

## integer(0)

SLR - Residual Analysis

Diagnostics plots are straightforward:

par(mfrow = c(2,2))
plot(fit)

  1. Tukey-Anscombe plot (is the variance of the errors Ei constant? Is the regression function correct?)
  2. Q-Q plot (are the errors Ei normally distributed?)
  3. Scale location plot (similar to Tukey-Anscombe plot)
  4. Leverage plot (what points have a strong influence on the fit?)

Residual plots by hand:

par(mfrow = c(1,2))
plot(fit$fitted,fit$resid) 

#Tukey-Anscombe
qqnorm(fit$resid) #Quantile-Quantile Plot
qqline(fit$resid) # adds the diagonal line

Some bad Tukey-Anscombe plots
Some bad Tukey-Anscombe plots

Multiple Linear Regression

Expand the simple linear model to more than one explanatory variable.

The Multiple Linear Regression Model
The Multiple Linear Regression Model
# Fit the model with lm
fitm <- lm(height ~ ph + l.sar, data = d.basisch)
summary(fitm)
## 
## Call:
## lm(formula = height ~ ph + l.sar, data = d.basisch)
## 
## Residuals:
##     Min      1Q  Median      3Q     Max 
## -4.1314 -0.4911  0.0849  0.6488  2.4754 
## 
## Coefficients:
##             Estimate Std. Error t value Pr(>|t|)    
## (Intercept)  26.9466     2.7445   9.818  < 2e-16 ***
## ph           -2.7558     0.3603  -7.649  5.6e-12 ***
## l.sar        -0.2519     0.2255  -1.117    0.266    
## ---
## Signif. codes:  0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1
## 
## Residual standard error: 1.007 on 120 degrees of freedom
## Multiple R-squared:  0.485,  Adjusted R-squared:  0.4764 
## F-statistic: 56.51 on 2 and 120 DF,  p-value: < 2.2e-16

MLR - Residual Analysis

# Look at the same plots as for simple linear regression
plot(fitm)

# It may help to plot the explanatory variables against the residuals.
plot(d.basisch$ph, fitm$resid)

plot(d.basisch$l.sar, fitm$resid)

Other

Graphics - Demo

demo(graphics)
## 
## 
##  demo(graphics)
##  ---- ~~~~~~~~
## 
## > #  Copyright (C) 1997-2009 The R Core Team
## > 
## > require(datasets)
## 
## > require(grDevices); require(graphics)
## 
## > ## Here is some code which illustrates some of the differences between
## > ## R and S graphics capabilities.  Note that colors are generally specified
## > ## by a character string name (taken from the X11 rgb.txt file) and that line
## > ## textures are given similarly.  The parameter "bg" sets the background
## > ## parameter for the plot and there is also an "fg" parameter which sets
## > ## the foreground color.
## > 
## > 
## > x <- stats::rnorm(50)
## 
## > opar <- par(bg = "white")
## 
## > plot(x, ann = FALSE, type = "n")

## 
## > abline(h = 0, col = gray(.90))
## 
## > lines(x, col = "green4", lty = "dotted")
## 
## > points(x, bg = "limegreen", pch = 21)
## 
## > title(main = "Simple Use of Color In a Plot",
## +       xlab = "Just a Whisper of a Label",
## +       col.main = "blue", col.lab = gray(.8),
## +       cex.main = 1.2, cex.lab = 1.0, font.main = 4, font.lab = 3)
## 
## > ## A little color wheel.    This code just plots equally spaced hues in
## > ## a pie chart.    If you have a cheap SVGA monitor (like me) you will
## > ## probably find that numerically equispaced does not mean visually
## > ## equispaced.  On my display at home, these colors tend to cluster at
## > ## the RGB primaries.  On the other hand on the SGI Indy at work the
## > ## effect is near perfect.
## > 
## > par(bg = "gray")
## 
## > pie(rep(1,24), col = rainbow(24), radius = 0.9)

## 
## > title(main = "A Sample Color Wheel", cex.main = 1.4, font.main = 3)
## 
## > title(xlab = "(Use this as a test of monitor linearity)",
## +       cex.lab = 0.8, font.lab = 3)
## 
## > ## We have already confessed to having these.  This is just showing off X11
## > ## color names (and the example (from the postscript manual) is pretty "cute".
## > 
## > pie.sales <- c(0.12, 0.3, 0.26, 0.16, 0.04, 0.12)
## 
## > names(pie.sales) <- c("Blueberry", "Cherry",
## +              "Apple", "Boston Cream", "Other", "Vanilla Cream")
## 
## > pie(pie.sales,
## +     col = c("purple","violetred1","green3","cornsilk","cyan","white"))

## 
## > title(main = "January Pie Sales", cex.main = 1.8, font.main = 1)
## 
## > title(xlab = "(Don't try this at home kids)", cex.lab = 0.8, font.lab = 3)
## 
## > ## Boxplots:  I couldn't resist the capability for filling the "box".
## > ## The use of color seems like a useful addition, it focuses attention
## > ## on the central bulk of the data.
## > 
## > par(bg="cornsilk")
## 
## > n <- 10
## 
## > g <- gl(n, 100, n*100)
## 
## > x <- rnorm(n*100) + sqrt(as.numeric(g))
## 
## > boxplot(split(x,g), col="lavender", notch=TRUE)

## 
## > title(main="Notched Boxplots", xlab="Group", font.main=4, font.lab=1)
## 
## > ## An example showing how to fill between curves.
## > 
## > par(bg="white")
## 
## > n <- 100
## 
## > x <- c(0,cumsum(rnorm(n)))
## 
## > y <- c(0,cumsum(rnorm(n)))
## 
## > xx <- c(0:n, n:0)
## 
## > yy <- c(x, rev(y))
## 
## > plot(xx, yy, type="n", xlab="Time", ylab="Distance")

## 
## > polygon(xx, yy, col="gray")
## 
## > title("Distance Between Brownian Motions")
## 
## > ## Colored plot margins, axis labels and titles.    You do need to be
## > ## careful with these kinds of effects.    It's easy to go completely
## > ## over the top and you can end up with your lunch all over the keyboard.
## > ## On the other hand, my market research clients love it.
## > 
## > x <- c(0.00, 0.40, 0.86, 0.85, 0.69, 0.48, 0.54, 1.09, 1.11, 1.73, 2.05, 2.02)
## 
## > par(bg="lightgray")
## 
## > plot(x, type="n", axes=FALSE, ann=FALSE)

## 
## > usr <- par("usr")
## 
## > rect(usr[1], usr[3], usr[2], usr[4], col="cornsilk", border="black")
## 
## > lines(x, col="blue")
## 
## > points(x, pch=21, bg="lightcyan", cex=1.25)
## 
## > axis(2, col.axis="blue", las=1)
## 
## > axis(1, at=1:12, lab=month.abb, col.axis="blue")
## 
## > box()
## 
## > title(main= "The Level of Interest in R", font.main=4, col.main="red")
## 
## > title(xlab= "1996", col.lab="red")
## 
## > ## A filled histogram, showing how to change the font used for the
## > ## main title without changing the other annotation.
## > 
## > par(bg="cornsilk")
## 
## > x <- rnorm(1000)
## 
## > hist(x, xlim=range(-4, 4, x), col="lavender", main="")

## 
## > title(main="1000 Normal Random Variates", font.main=3)
## 
## > ## A scatterplot matrix
## > ## The good old Iris data (yet again)
## > 
## > pairs(iris[1:4], main="Edgar Anderson's Iris Data", font.main=4, pch=19)

## 
## > pairs(iris[1:4], main="Edgar Anderson's Iris Data", pch=21,
## +       bg = c("red", "green3", "blue")[unclass(iris$Species)])

## 
## > ## Contour plotting
## > ## This produces a topographic map of one of Auckland's many volcanic "peaks".
## > 
## > x <- 10*1:nrow(volcano)
## 
## > y <- 10*1:ncol(volcano)
## 
## > lev <- pretty(range(volcano), 10)
## 
## > par(bg = "lightcyan")
## 
## > pin <- par("pin")
## 
## > xdelta <- diff(range(x))
## 
## > ydelta <- diff(range(y))
## 
## > xscale <- pin[1]/xdelta
## 
## > yscale <- pin[2]/ydelta
## 
## > scale <- min(xscale, yscale)
## 
## > xadd <- 0.5*(pin[1]/scale - xdelta)
## 
## > yadd <- 0.5*(pin[2]/scale - ydelta)
## 
## > plot(numeric(0), numeric(0),
## +      xlim = range(x)+c(-1,1)*xadd, ylim = range(y)+c(-1,1)*yadd,
## +      type = "n", ann = FALSE)

## 
## > usr <- par("usr")
## 
## > rect(usr[1], usr[3], usr[2], usr[4], col="green3")
## 
## > contour(x, y, volcano, levels = lev, col="yellow", lty="solid", add=TRUE)
## 
## > box()
## 
## > title("A Topographic Map of Maunga Whau", font= 4)
## 
## > title(xlab = "Meters North", ylab = "Meters West", font= 3)
## 
## > mtext("10 Meter Contour Spacing", side=3, line=0.35, outer=FALSE,
## +       at = mean(par("usr")[1:2]), cex=0.7, font=3)
## 
## > ## Conditioning plots
## > 
## > par(bg="cornsilk")
## 
## > coplot(lat ~ long | depth, data = quakes, pch = 21, bg = "green3")

## 
## > par(opar)
demo(image)
## 
## 
##  demo(image)
##  ---- ~~~~~
## 
## > #  Copyright (C) 1997-2009 The R Core Team
## > 
## > require(datasets)
## 
## > require(grDevices); require(graphics)
## 
## > x <- 10*(1:nrow(volcano)); x.at <- seq(100, 800, by=100)
## 
## > y <- 10*(1:ncol(volcano)); y.at <- seq(100, 600, by=100)
## 
## >                    # Using Terrain Colors
## > 
## > image(x, y, volcano, col=terrain.colors(100),axes=FALSE)

## 
## > contour(x, y, volcano, levels=seq(90, 200, by=5), add=TRUE, col="brown")
## 
## > axis(1, at=x.at)
## 
## > axis(2, at=y.at)
## 
## > box()
## 
## > title(main="Maunga Whau Volcano", sub = "col=terrain.colors(100)", font.main=4)
## 
## >                    # Using Heat Colors
## > 
## > image(x, y, volcano, col=heat.colors(100), axes=FALSE)

## 
## > contour(x, y, volcano, levels=seq(90, 200, by=5), add=TRUE, col="brown")
## 
## > axis(1, at=x.at)
## 
## > axis(2, at=y.at)
## 
## > box()
## 
## > title(main="Maunga Whau Volcano", sub = "col=heat.colors(100)", font.main=4)
## 
## >                    # Using Gray Scale
## > 
## > image(x, y, volcano, col=gray(100:200/200), axes=FALSE)

## 
## > contour(x, y, volcano, levels=seq(90, 200, by=5), add=TRUE, col="black")
## 
## > axis(1, at=x.at)
## 
## > axis(2, at=y.at)
## 
## > box()
## 
## > title(main="Maunga Whau Volcano \n col=gray(100:200/200)", font.main=4)
## 
## > ## Filled Contours are even nicer sometimes :
## > example(filled.contour)
## 
## flld.c> require("grDevices") # for colours
## 
## flld.c> filled.contour(volcano, asp = 1) # simple

## 
## flld.c> x <- 10*1:nrow(volcano)
## 
## flld.c> y <- 10*1:ncol(volcano)
## 
## flld.c> filled.contour(x, y, volcano,
## flld.c+     color.palette = function(n) hcl.colors(n, "terrain"),
## flld.c+     plot.title = title(main = "The Topography of Maunga Whau",
## flld.c+     xlab = "Meters North", ylab = "Meters West"),
## flld.c+     plot.axes = { axis(1, seq(100, 800, by = 100))
## flld.c+                   axis(2, seq(100, 600, by = 100)) },
## flld.c+     key.title = title(main = "Height\n(meters)"),
## flld.c+     key.axes = axis(4, seq(90, 190, by = 10)))  # maybe also asp = 1

## 
## flld.c> mtext(paste("filled.contour(.) from", R.version.string),
## flld.c+       side = 1, line = 4, adj = 1, cex = .66)
## 
## flld.c> # Annotating a filled contour plot
## flld.c> a <- expand.grid(1:20, 1:20)
## 
## flld.c> b <- matrix(a[,1] + a[,2], 20)
## 
## flld.c> filled.contour(x = 1:20, y = 1:20, z = b,
## flld.c+                plot.axes = { axis(1); axis(2); points(10, 10) })

## 
## flld.c> ## Persian Rug Art:
## flld.c> x <- y <- seq(-4*pi, 4*pi, length.out = 27)
## 
## flld.c> r <- sqrt(outer(x^2, y^2, `+`))
## 
## flld.c> ## "minimal"
## flld.c> filled.contour(cos(r^2)*exp(-r/(2*pi)), axes = FALSE, key.border=NA)

## 
## flld.c> ## rather, the key *should* be labeled (but axes still not):
## flld.c> filled.contour(cos(r^2)*exp(-r/(2*pi)), frame.plot = FALSE,
## flld.c+                plot.axes = {})

demo(persp)
## 
## 
##  demo(persp)
##  ---- ~~~~~
## 
## > ### Demos for  persp()  plots   -- things not in  example(persp)
## > ### -------------------------
## > 
## > require(datasets)
## 
## > require(grDevices); require(graphics)
## 
## > ## (1) The Obligatory Mathematical surface.
## > ##     Rotated sinc function.
## > 
## > x <- seq(-10, 10, length.out = 50)
## 
## > y <- x
## 
## > rotsinc <- function(x,y)
## + {
## +     sinc <- function(x) { y <- sin(x)/x ; y[is.na(y)] <- 1; y }
## +     10 * sinc( sqrt(x^2+y^2) )
## + }
## 
## > sinc.exp <- expression(z == Sinc(sqrt(x^2 + y^2)))
## 
## > z <- outer(x, y, rotsinc)
## 
## > oldpar <- par(bg = "white")
## 
## > persp(x, y, z, theta = 30, phi = 30, expand = 0.5, col = "lightblue")

## 
## > title(sub=".")## work around persp+plotmath bug
## 
## > title(main = sinc.exp)
## 
## > persp(x, y, z, theta = 30, phi = 30, expand = 0.5, col = "lightblue",
## +       ltheta = 120, shade = 0.75, ticktype = "detailed",
## +       xlab = "X", ylab = "Y", zlab = "Z")

## 
## > title(sub=".")## work around persp+plotmath bug
## 
## > title(main = sinc.exp)
## 
## > ## (2) Visualizing a simple DEM model
## > 
## > z <- 2 * volcano        # Exaggerate the relief
## 
## > x <- 10 * (1:nrow(z))   # 10 meter spacing (S to N)
## 
## > y <- 10 * (1:ncol(z))   # 10 meter spacing (E to W)
## 
## > persp(x, y, z, theta = 120, phi = 15, scale = FALSE, axes = FALSE)

## 
## > ## (3) Now something more complex
## > ##     We border the surface, to make it more "slice like"
## > ##     and color the top and sides of the surface differently.
## > 
## > z0 <- min(z) - 20
## 
## > z <- rbind(z0, cbind(z0, z, z0), z0)
## 
## > x <- c(min(x) - 1e-10, x, max(x) + 1e-10)
## 
## > y <- c(min(y) - 1e-10, y, max(y) + 1e-10)
## 
## > fill <- matrix("green3", nrow = nrow(z)-1, ncol = ncol(z)-1)
## 
## > fill[ , i2 <- c(1,ncol(fill))] <- "gray"
## 
## > fill[i1 <- c(1,nrow(fill)) , ] <- "gray"
## 
## > par(bg = "lightblue")
## 
## > persp(x, y, z, theta = 120, phi = 15, col = fill, scale = FALSE, axes = FALSE)

## 
## > title(main = "Maunga Whau\nOne of 50 Volcanoes in the Auckland Region.",
## +       font.main = 4)
## 
## > par(bg = "slategray")
## 
## > persp(x, y, z, theta = 135, phi = 30, col = fill, scale = FALSE,
## +       ltheta = -120, lphi = 15, shade = 0.65, axes = FALSE)

## 
## > ## Don't draw the grid lines :  border = NA
## > persp(x, y, z, theta = 135, phi = 30, col = "green3", scale = FALSE,
## +       ltheta = -120, shade = 0.75, border = NA, box = FALSE)

## 
## > ## `color gradient in the soil' :
## > fcol <- fill ; fcol[] <- terrain.colors(nrow(fcol))
## 
## > persp(x, y, z, theta = 135, phi = 30, col = fcol, scale = FALSE,
## +       ltheta = -120, shade = 0.3, border = NA, box = FALSE)

## 
## > ## `image like' colors on top :
## > fcol <- fill
## 
## > zi <- volcano[ -1,-1] + volcano[ -1,-61] +
## +            volcano[-87,-1] + volcano[-87,-61]  ## / 4
## 
## > fcol[-i1,-i2] <-
## +     terrain.colors(20)[cut(zi,
## +                            stats::quantile(zi, seq(0,1, length.out = 21)),
## +                            include.lowest = TRUE)]
## 
## > persp(x, y, 2*z, theta = 110, phi = 40, col = fcol, scale = FALSE,
## +       ltheta = -120, shade = 0.4, border = NA, box = FALSE)

## 
## > ## reset par():
## > par(oldpar)
pacman::p_load(scatterplot3d); example(scatterplot3d)
## 
## scttr3>   ## On some devices not all colors can be displayed.
## scttr3>   ## Try the postscript device or use highlight.3d = FALSE.
## scttr3> 
## scttr3>   ## example 1
## scttr3>   z <- seq(-10, 10, 0.01)
## 
## scttr3>   x <- cos(z)
## 
## scttr3>   y <- sin(z)
## 
## scttr3>   scatterplot3d(x, y, z, highlight.3d=TRUE, col.axis="blue",
## scttr3+       col.grid="lightblue", main="scatterplot3d - 1", pch=20, mar=c(0,0,0,0))

## 
## scttr3>   ## example 2
## scttr3>   temp <- seq(-pi, 0, length = 50)
## 
## scttr3>   x <- c(rep(1, 50) %*% t(cos(temp)))
## 
## scttr3>   y <- c(cos(temp) %*% t(sin(temp)))
## 
## scttr3>   z <- c(sin(temp) %*% t(sin(temp)))
## 
## scttr3>   scatterplot3d(x, y, z, highlight.3d=TRUE,
## scttr3+       col.axis="blue", col.grid="lightblue",
## scttr3+       main="scatterplot3d - 2", pch=20)

## 
## scttr3>   ## example 3
## scttr3>   temp <- seq(-pi, 0, length = 50)
## 
## scttr3>   x <- c(rep(1, 50) %*% t(cos(temp)))
## 
## scttr3>   y <- c(cos(temp) %*% t(sin(temp)))
## 
## scttr3>   z <- 10 * c(sin(temp) %*% t(sin(temp)))
## 
## scttr3>   color <- rep("green", length(x))
## 
## scttr3>   temp <- seq(-10, 10, 0.01)
## 
## scttr3>   x <- c(x, cos(temp))
## 
## scttr3>   y <- c(y, sin(temp))
## 
## scttr3>   z <- c(z, temp)
## 
## scttr3>   color <- c(color, rep("red", length(temp)))
## 
## scttr3>   scatterplot3d(x, y, z, color, pch=20, zlim=c(-2, 10),
## scttr3+       main="scatterplot3d - 3")

## 
## scttr3>   ## example 4
## scttr3>   my.mat <- matrix(runif(25), nrow=5)
## 
## scttr3>   dimnames(my.mat) <- list(LETTERS[1:5], letters[11:15])
## 
## scttr3>   my.mat # the matrix we want to plot ...
##           k         l         m          n          o
## A 0.1563748 0.2371518 0.8191526 0.99730158 0.80676768
## B 0.3004088 0.3492321 0.9257641 0.49034417 0.94911539
## C 0.8892683 0.5387822 0.7769605 0.98618686 0.09528478
## D 0.2299601 0.8143910 0.3439360 0.66268003 0.01587171
## E 0.5235825 0.4243346 0.4084683 0.07414848 0.76256849
## 
## scttr3>   s3d.dat <- data.frame(cols=as.vector(col(my.mat)),
## scttr3+       rows=as.vector(row(my.mat)),
## scttr3+       value=as.vector(my.mat))
## 
## scttr3>   scatterplot3d(s3d.dat, type="h", lwd=5, pch=" ",
## scttr3+       x.ticklabs=colnames(my.mat), y.ticklabs=rownames(my.mat),
## scttr3+       color=grey(25:1/40), main="scatterplot3d - 4")

## 
## scttr3>   ## example 5
## scttr3>   data(trees)
## 
## scttr3>   s3d <- scatterplot3d(trees, type="h", highlight.3d=TRUE,
## scttr3+       angle=55, scale.y=0.7, pch=16, main="scatterplot3d - 5")

## 
## scttr3>   # Now adding some points to the "scatterplot3d"
## scttr3>   s3d$points3d(seq(10,20,2), seq(85,60,-5), seq(60,10,-10),
## scttr3+       col="blue", type="h", pch=16)
## 
## scttr3>   # Now adding a regression plane to the "scatterplot3d"
## scttr3>   attach(trees)
## 
## scttr3>   my.lm <- lm(Volume ~ Girth + Height)
## 
## scttr3>   s3d$plane3d(my.lm, lty.box = "solid")
## 
## scttr3>   ## example 6; by Martin Maechler
## scttr3>   cubedraw <- function(res3d, min = 0, max = 255, cex = 2, text. = FALSE)
## scttr3+   {
## scttr3+     ## Purpose: Draw nice cube with corners
## scttr3+     cube01 <- rbind(c(0,0,1), 0, c(1,0,0), c(1,1,0), 1, c(0,1,1), # < 6 outer
## scttr3+                     c(1,0,1), c(0,1,0)) # <- "inner": fore- & back-ground
## scttr3+     cub <- min + (max-min)* cube01
## scttr3+     ## visibile corners + lines:
## scttr3+     res3d$points3d(cub[c(1:6,1,7,3,7,5) ,], cex = cex, type = 'b', lty = 1)
## scttr3+     ## hidden corner + lines
## scttr3+     res3d$points3d(cub[c(2,8,4,8,6),     ], cex = cex, type = 'b', lty = 3)
## scttr3+     if(text.)## debug
## scttr3+         text(res3d$xyz.convert(cub), labels=1:nrow(cub), col='tomato', cex=2)
## scttr3+   }
## 
## scttr3>   ## 6 a) The named colors in R, i.e. colors()
## scttr3>   cc <- colors()
## 
## scttr3>   crgb <- t(col2rgb(cc))
## 
## scttr3>   par(xpd = TRUE)
## 
## scttr3>   rr <- scatterplot3d(crgb, color = cc, box = FALSE, angle = 24,
## scttr3+       xlim = c(-50, 300), ylim = c(-50, 300), zlim = c(-50, 300))

## 
## scttr3>   cubedraw(rr)
## 
## scttr3>   ## 6 b) The rainbow colors from rainbow(201)
## scttr3>   rbc <- rainbow(201)
## 
## scttr3>   Rrb <- t(col2rgb(rbc))
## 
## scttr3>   rR <- scatterplot3d(Rrb, color = rbc, box = FALSE, angle = 24,
## scttr3+       xlim = c(-50, 300), ylim = c(-50, 300), zlim = c(-50, 300))

## 
## scttr3>   cubedraw(rR)
## 
## scttr3>   rR$points3d(Rrb, col = rbc, pch = 16)
example(points)
## 
## points> require(stats) # for rnorm
## 
## points> plot(-4:4, -4:4, type = "n")  # setting up coord. system

## 
## points> points(rnorm(200), rnorm(200), col = "red")
## 
## points> points(rnorm(100)/2, rnorm(100)/2, col = "blue", cex = 1.5)
## 
## points> op <- par(bg = "light blue")
## 
## points> x <- seq(0, 2*pi, length.out = 51)
## 
## points> ## something "between type='b' and type='o'":
## points> plot(x, sin(x), type = "o", pch = 21, bg = par("bg"), col = "blue", cex = .6,
## points+  main = 'plot(..., type="o", pch=21, bg=par("bg"))')

## 
## points> par(op)
## 
## points> ## Illustration of pch = 0:25 (as in the figure shown above in PDF/HTML help)
## points> ## Not run: png("pch.png", height = 0.7, width = 7, res = 100, units = "in")
## points> par(mar = rep(0,4))
## 
## points> plot(c(-1, 26), 0:1, type = "n", axes = FALSE)

## 
## points> text(0:25, 0.6, 0:25, cex = 0.5)
## 
## points> points(0:25, rep(0.3, 26), pch = 0:25, bg = "grey")
## 
## points> ##-------- Showing all the extra & some char graphics symbols ---------
## points> pchShow <-
## points+   function(extras = c("*",".", "o","O","0","+","-","|","%","#"),
## points+            cex = 3, ## good for both .Device=="postscript" and "x11"
## points+            col = "red3", bg = "gold", coltext = "brown", cextext = 1.2,
## points+            main = paste("plot symbols :  points (...  pch = *, cex =",
## points+                         cex,")"))
## points+   {
## points+     nex <- length(extras)
## points+     np  <- 26 + nex
## points+     ipch <- 0:(np-1)
## points+     k <- floor(sqrt(np))
## points+     dd <- c(-1,1)/2
## points+     rx <- dd + range(ix <- ipch %/% k)
## points+     ry <- dd + range(iy <- 3 + (k-1)- ipch %% k)
## points+     pch <- as.list(ipch) # list with integers & strings
## points+     if(nex > 0) pch[26+ 1:nex] <- as.list(extras)
## points+     plot(rx, ry, type = "n", axes  =  FALSE, xlab = "", ylab = "", main = main)
## points+     abline(v = ix, h = iy, col = "lightgray", lty = "dotted")
## points+     for(i in 1:np) {
## points+       pc <- pch[[i]]
## points+       ## 'col' symbols with a 'bg'-colored interior (where available) :
## points+       points(ix[i], iy[i], pch = pc, col = col, bg = bg, cex = cex)
## points+       if(cextext > 0)
## points+           text(ix[i] - 0.3, iy[i], pc, col = coltext, cex = cextext)
## points+     }
## points+   }
## 
## points> pchShow()

## 
## points> pchShow(c("o","O","0"), cex = 2.5)

## 
## points> pchShow(NULL, cex = 4, cextext = 0, main = NULL)

## 
## points> ## No test: 
## points> ##D ## ------------ test code for various pch specifications -------------
## points> ##D # Try this in various font families (including Hershey)
## points> ##D # and locales.  Use sign = -1 asserts we want Latin-1.
## points> ##D # Standard cases in a MBCS locale will not plot the top half.
## points> ##D TestChars <- function(sign = 1, font = 1, ...)
## points> ##D {
## points> ##D    MB <- l10n_info()$MBCS
## points> ##D    r <- if(font == 5) { sign <- 1; c(32:126, 160:254)
## points> ##D        } else if(MB) 32:126 else 32:255
## points> ##D    if (sign == -1) r <- c(32:126, 160:255)
## points> ##D    par(pty = "s")
## points> ##D    plot(c(-1,16), c(-1,16), type = "n", xlab = "", ylab = "",
## points> ##D         xaxs = "i", yaxs = "i",
## points> ##D         main = sprintf("sign = %d, font = %d", sign, font))
## points> ##D    grid(17, 17, lty = 1) ; mtext(paste("MBCS:", MB))
## points> ##D    for(i in r) try(points(i%%16, i%/%16, pch = sign*i, font = font,...))
## points> ##D }
## points> ##D TestChars()
## points> ##D try(TestChars(sign = -1))
## points> ##D TestChars(font = 5)  # Euro might be at 160 (0+10*16).
## points> ##D                      # macOS has apple at 240 (0+15*16).
## points> ##D try(TestChars(-1, font = 2))  # bold
## points> ## End(No test)
## points> 
## points>